Process for sweetening hydrocarbon oils



Patented July 16, 1940 UNITED STATES PROCESS FOR SWEETENING HYDRO- CABBON OILS I Charles M. Blair, Jr., Webster Groves, Mo., and Ira S. Boydstun, Fort Worth, Tex., assignors to Petrolite Corporation, Ltd., Wilmington, Del., a corporation ofDelaware No Drawing.

Application October 28, 1939, Serial No. 301,829

15 Claims. (Ol. 196-33) Our invention relates to the sweetening of hydrocarbon oils and more particularly has reference to improvements in the conventional doctor treatment for the removal of mercaptans from light hydrocarbon distillates such as gasoline, naphtha, kerosene, benzine and petroleum oils in general.

It is a principal object of the invention to render the doctor treatment more rapid and economical and to produce sweetened distillates of unusually desirable properties.

The doctor treatment has long been applied to petroleum oils for the removal of mercaptans. It involves treatment of the oils with elementary sulfur and an aqueous alkaline solution of sodium plumbite, known as the doctor solution." The plumbite solution effects a chemical reaction between the mercaptans and the elementary sulfur, resulting in the conversion of the mercaptans to dialkyl disulfides and also into some trisulfide, while the sulfur is converted mainly into sulfides, polysulfides, thiosulfates, etc.

In practicing the conventional doctor treatment, an excess of elementary sulfur is used to bring about a break, a term used in the art to indicate the settling or subsidence point in the doctor treatment. That is to say, the amount of free sulfur used is in excess ofthe theoretical quantity required to convert the mercaptans into disulfides and other innocuous compounds, the excess serving to induce the break in the treatment. Such use of elementary sulfur to effect settling or subsidence results in the incorporation of sulfur into the distillate, with its attendant objections. Among these objections, in the case of gasoline, are poor inhibitor and tetraethyl lead susceptibility, lowered anti-knock value, increased corrosive action on metals, poor color and odor stability, and increased tendency to form. gum. a Although doctor treatment in its many variations is well understood in the art, it may be well to emphasize, by a suitable reference, the circumstances and conditions attending a break and the difliculty of coagulating the colloidal black precipitate.

Doctor plants differ in the way in which doctor solution and sulfur are mixed with the gasoline and the length of time they remain in contact. It is common practice to add the sulfur in gasoline solution before, at the same time as, or after the gasoline and doctor solutions are mixed. The mixing may be done by orifice plates, baiiled pipes, pipes with right-angle bends, or

mechanical mixing devices, and mixing time may vary from a few seconds to several minutes.

When sulfur is added to a mixture of gasoline and doctor solution, the oil becomes orangered in color; after a longer or shorter time, depending on the gasoline and the amount of sulfur added, thebreak takes place, when the color disappears and a red-brown to black precipitate, usually called lead sulfide, forms and settles.

In different plants, the break may be produced as the gasoline leaves the mixers or it may not occur until after the gasoline has entered the settling drum. If a plant has adequate mixing (the proper time of mixing will depend on the type of gasoline and somewhat on the degree of sourness), the gasoline may be allowed to break as it leaves the mixers, and the amount of sulfur required to do this will not be so great as to harm inhibitor susceptibility. However, if a plant has little mixing equipment (a common installation is three mixing nozzles in about six feet of line, which for most gasoline is much less mixing than is desirable), a break cannot be obtained in the mixers without using a considerable excess of sulfur, with consequent detriment to the inhibitor effectiveness. If, however, the break in such plants occurs in the first settler from three to fifteen minutes after the gasoline leaves the mixers, the results from an inhibitor standpoint will usually be satisfactory. But when the break occurs in the settler, the gasoline being no longer in contact with doctor solution, it tends to produce a finer precipitate, settling more slowly than when the gasoline is broken out while still in contact with doctor solution. As plants deficient in mixing equipment are also often lacking in settling capacity, the treater in such cases faces a serious dilemma. If he uses excess,sulfur, his gasoline settles well but inhibitor susceptibility is poor; if sulfur is kept down, the gasoline breaks and settles slowly and lead sulfide leaves the plant suspended in the gasoline. (Industrial & Engineering Chemistry, vol. 30, No. 11, Nov. 1938, p. 1276) Thus, in actual practice, the present trend has been to continue to use sulfur as a break inducer, insofar that no universal andeconomic solution of the problem has been heretofore available. Some effort has been made to solve the problem by subsequent washing with aqueous solution, but this has resulted in attendant loss of expensive lead. Another approach to the problem concerned the use of sodium oleate, sodium resinate, sodium stearate, sodium palmitate, and other simple unmodified fatty materials as break inducers for replacing a part of the sulfur which is ordinarily used as a break inducer. It is not believed that such procedure is ordinarily applicable as a complete substitute for sulfur as a break inducer. Or, in other words, it is not believed that any attempt has been made to apply such process in instances where the amount of elementary sulfur represented only theoretical quantities and which would necessitate that the simple fatty materials, such as soap, be vrelied upon solely as the break inducer.

We have now found that the salts of the sulfated and phosphoratedfatty acids and fatty oils possess the property of inducing a break in the doctor treatment and our invention involves their use, in the sweetening of sour oils by. means of plumbite solution and elementary sulfur, to effect the settling or subsidence in the known sweetening process.

The preferred break-inducers of our invention are the salts of fatty acid sulfates or sulfonates, commonly known as sulfated oils, sulfonated oils, Turkey red oils, sulfurized fatty oils, sulfurized fatty acids, sulfonized oils, etc. These reagents have been employed in the textile industry for many years and are well-known articles of commerce. They are commonly prepared by treating fatty oils, such as castor oil, olive oil, arachis oil, cod oil, or the like with sulfuric acid, followed by washing with water or asalt solution, and neutralization with ammonia or a base. Fatty acids are often used in place of fatty oils in the preparation of Turkey red oils, oleic acid, for example, being frequently employed. The manufacture and properties of these sulfated oils or Turkey red oils are described in many places throughout the literature, for example, in Lewkowitsch, Chemical Technology of Oils, Fats and Waxes, sixth edition, volume 3, page 207 et. seq.

The reactions involved in the preparation of sulfated oils are quire complex. The initial product obtained on treating the fatty oil or fatty acid with sulfuric acid is apparently a true fatty acid hydrogen sulfate. On washing out the excess acid with water or salt solution, some hydrolysis and decomposition usually takes place with lowering of the percentage of organically combined S03. In addition, reactions occur leading to the formation of esters, estolides, ethers, and lactones, the actual composition depending upon the particular fat or fatty acid employed, the concentration of sulfuric acid used, the temperature at which the reaction is conducted, the temperature at whichthe washing is conducted, etc,

The'sulfated oil finally obtained may contain very little combined sulfur, often as little as 0.15%, expressed as $03. However, sulfated oils are sometimes prepared containing as much as 12% or even 15% of combined $03. The products contemplated for use in the present process may, then, -contain from about 0.15% to about 15% of combined S03, but theproducts most commonly used will range in combined SO: content from about 1% to 5%.

Products similar in properties to sulfated oils may be prepared by treating fatty oils or fatty acids with phosphoric acid. We have found that these so-called phosphorated oils" are also efficient break inducers and are therefore suitable for use in the sweetening process.

Sulfated oils or Turkey red oils as usually prepared are neutralized with ammonia, sodium hydroxide, or other cheap base, to a point slightly alkaline to the methyl orange endpoint. This leaves the carboxylic hydrogens of the product ethyl or butyl mercaptan.

unneutraliz'ed. The product so neutralized is the -one commonly employed in the present process.

However, if desired, the completely neutralized product may be used orthe unneutralized acid sulfate itself may be used. Obviously, if the unneutralized or partially neutralized products are used, they are converted into the completely neutralized form on contact with the strongly alkaline doctor solution. Therefore, in the appended claims, the reference to the use of salts includes the use of the sulfated or phosphorated product in the unneutralized or partially neutralized forms. Also, salts other than the sodium or ammonium salts may be employed. For example, the amylamine salt, the triethanolamine salt, the cyclohexylamin'e salt, the methylamine salt, and the like may be used. Such salts may in some cases be oil soluble and therefore particularly adapted for use where it is desirable to dissolve the break inducer in the hydrocarbon oil which is being sweetened.

The compounds herein disclosed are preferably used as the sole break inducer for the doctor treatment, in which event the quantity of elementary sulfur employed in the doctor treatment is not in excess of the theoretical amount required to convert the mercaptans. In this preferred operation, where no appreciableexcess of sulfur is used in the doctor treatment, there is effected a faster break than can be obtained by means of. other break inducers and. frequently a break is effected where one might not be otherwise obtainable. Additionally, there is recovered a distillate which is free of excess sulfur, an important advantage as has already been indicated.

However, the invention is not limited to the use of the organic compounds referred to as the sole break inducer but they may be employed in conjunction with other substances having a like property, such as elementary sulfur. In operation of this type, a small excess of sulfur would be used in the doctor treatment, the excess functioning with the compounds of this invention to bring about the desired break in the treatment. The advantages of such operation are that relatively little sulfur is required, the break is induced very rapidly, and frequently a break is effected where one cannot be obtained at all by means of sulfur alone.

As to the preferred operation above indicated, it will be observed that the doctor treatment differs from that heretofore employed in that the quantity of elementary sulfur added is only the theoretical amount based on stoichiometrical calculations, or other comparable test, to convert mercaptans to disulfides and other innocuous compounds, there being present during the treatment no excess of sulfur capable of completely or partially acting as a break inducer. Elementary sulfur, if present in sufficient excess in the sweetened distillate, can be detected by the doctor test with the addition of a mercaptan such as For instance, a sweetened gasoline containing an excess of elementary sulfur no longer shows positive in the doctor test. However, if there is a slight excess of elementary sulfur present, this elementary sulfur can be detected by 'the addition of butyl mercaptan or the like, followed by a doctor test on the admixture. A large excess may be indicated by the less sensitive copper strip test.

The butyl mercaptan test, referred to above, is commonlyused in a qualitative manner to detect excess elementary sulfur. This test is described in the Universal 011 Products Co. Bulletin No. 22, D. 15, as follows: I

In doctor sweetening, the most important fac-- tor in securing inhibitor effectiveness, is to use the smallest possible amount of sulfur. Sulfur addition may be controlled by testing with mercury or butyl mercaptan. In making the butyl mercaptan test, a sample of gasoline drawn from the doctor plant after it has left the mixers is allowed to stand until the lead sulfide has settled, and 30 cc. filtered into a 4 ounce oil sample bottle. 20 cc. of a 1 to 1,400 solution of butyl mercaptan is added and 10 cc. of doctor solution. The mixture is shaken for 15 seconds and observed. The sample should be green-yellow. It will slowly become opaque but should remain yellow in color even if observed for 30 minutes. If it turns orange or brown, excess sulfur has been used, and on addition of inhibitor the gasoline will have lower induction period and higher copper dish'gum than would have resulted had less sulfur been used."

The chemistry of the reactions which enter into doctor sweetening is rather complex and not completely understood. However, it is common practice, for the purpose of calculating the amount of sulfur necessary, to use the following reaction as being representative:

Wherein R represents the hydrocarbon group of a mercaptan or disulflde.

The amount of sulfur required for completion of these reactions may be calculated from the original mercaptan content of the distillate. With some distillates, the sweetening reaction appears to lead to the formation of stable trisulfides, rather than disulfidcs. In this case the reactions presumably proceed as follows:

With distillates where these reactions take place, the theoretical sulfur requirement may be calculated by use of the above equations and the known original mercaptan content of the distillate. However, for all practical purposes, the butyl mercaptan test, previously described, may be used as a test for whether or not excess sulfur has been used. Accordingly, the term negative to the butyl mercaptan tes as applied to sweetened distillates, is used herein to mean that a distillate has been sweetened with the theoretical amount of sulfur, or that the minimum amount of sulfur necessary for completion of the sweetening reaction has been employed. The reason for this is that the butyl mercaptan test may be made more easily and more quickly than a, determination of the actual course or nature of the sweetening reactions.

As is understood, of course, if hydrogen sulfide is present, allowance must be made for the amount of lead required to remove such sulfide. However, this is not apt to be a factor requiring consideration, due to usual preliminary removal of hydrogen sulfide.

In view of what has been said previously, it is obvious that the satisfactory application of the doctor treatment must involve a rapid and complete separation of lead sulfide and associated insoluble material, as soon as the mercaptans are converted into disulfides or other more innocuous compounds. Although the above reactions indicate only precipitation of lead sulfide, it has been found that in reality a precipitate may contaln a comparatively small amount of lead sulfide; and there may also be present-various complex materials, part of which at least are organic in nature and may represent basic mercaptides. The equations indicate that the amount of elementary sulfur to be added per pound of combined sulfur present as mercaptan should be in the ratio of one-half to one. In actual practice, however, with the conventional doctortreatment, the quantity of sulfur added for complete reaction, and particularly to give subsidence or settling of the black precipitate, is not so definite. As a matter of common practice, sulfur is added in the conventional doctor treatment for two distinct purposes of converting mercaptans and inducing the break; and these two purposes must be fully appreciated in order to understand the benefit obtained by applying the improved procedure which constitutes our present invention, particularly in its preferable form, i. e., where the complex organic compounds herein described are used as the sole break inducer, with only the theoretical amount of sulfur to convert mercaptans or to give a negative butyl mercaptan test.

It has heretofore been proposed to employ water soluble soaps to effect the break in doctor treatment, the soaps being utilized in ratios of l to 2500 or 1 to 7500. At such ratios, the common soaps are often inefiective and hence there is the tendency to employ just as much sulfur as if no soap had been added. In contradistinction to the common soaps heretofore contemplated, the break inducers of the present invention are invariably effective and invariably enable a marked reduction in the amount of sulfur needed in the doctor treatment, even to the extent, as in the preferred embodiment already described, of limiting the sulfur to the theoretical amount necessary for converting the mercaptans into innocuous compounds.

The break inducers of this invention need be used in only very minute quantities, for example, in ratios varying from 1 to 5000 or 1 to 75000 or even 1 to 75,000, based on recovered or sweetened gasoline or other distillate treated. To the extent that our improved break inducers possess the property of forming oil-in-water emulsions, it should be observed that they are employed in such insignificant quantities that they do not exhibit any detectable or appreciable emulsifying action.

Although our invention can be applied to any variation of the conventional doctor treatment in a manner which is most convenient under the specific conditions surrounding the particular operation, for purposes of brevity, we will describe only the preferable form of procedure, i. e., where the herein disclosed organic compounds are used as sole break inducers. It is obvious, however, that those skilled in the art and acquainted with such procedure could readily modify the conventional doctor treatment in which elementary sulfur is used as a break inducer, so as to reduce the amount of sulfur employed, and offset that reduction by suitable quantities of the break inducers of this invention.

done by means of a small injector pump adjusted to deliver the break inducer in some definite, desired amount, usually within the limits of one part per 7500 to 75,000 parts of gasoline. After the introduction. of break inducer has begun, the

' amount of sulfur added to the distillate, or to the mixture of distillate and doctor solution, is'decreased to the theoretical amount.

In batch system doctor sweetening plants, the required amount of break inducer is introduced into the sour distillate and mixed thoroughly before the treatment with doctor solution and sulfur. In this case, also, the amount of sulfur used is reduced to the theoretical amount. 7

Sometimes better results are obtained if the break'inducer is added to the doctor solution or to the distillate after the latter has been mixed with doctor solution and sulfur. Regardless of the point of introduction of the break inducer, however, the amount of sulfur required for completion of the sweetening reactions and subsidence of the black precipitate is reduced to, or nearly to, the theoretical amount.

The doctor solution used for sweetening is generally regenerated after each use and employed for sweetening further amounts of sour distillate. Where the break inducer has been added to the doctor solution, its activity may persist thru one or more regenerations, but eventually further amounts will have to be added. The number of volumes of distillate sweetened per volume of break inducer used in the doctor solution usually will be more than 7500, and the ratio of break inducer may average one part to 25,000 parts sweetened distillate.

In order to illustrate the effectiveness of the complex organic materials employed as break inducers, the following table is included. This table includes the results obtained on the -gaso line produced from Louisiana and Arkansas crudes andis typical of a number of similar tests obtained on the wide varieties of gasoline derived from other sources and produced in various refineries, and is also typical of actual plant operin order to complete the chemical reactions. On the other hand, the addition of 17% excess of sulfur, i. e., the use of? milligrams of elementary sulfur, did not give a break. However, when'the amount of sulfur used was increased to 8 miligrams, 1. e., a 33%% excess, then a perfectly satisfactory break was obtained. Obviously such excess of elementary sulfur resulted in a positive butyl mercaptan test. When an eifort was made to 'substitutethe common soap type of break inducer for elementary sulfur, it was found that its use, in amount equivalent to 10 times the amount of sulfur required for break induction, did not give satisfactory results. For instance, when the 2 milligram excess of elementary sulfur was replaced by 20 -milligrams of sodium stearate, the break obtained was only fair. This same-condition prevailed when a similar amount of sodium oleate or sodium resinate was employed. Only in the case of castile soap were results obtained which could be characterized as good; i. e., sufllciently satisfactory to indicate they would be satisfactory under practically all plant conditions. However, when the amount of sulfur used was only theoretical, that is only six milligrams, and when an effort was made to rely upon the simple break inducers solely for break induction, then it is to be noted that absolutely no break was obtained. In other words, if one adds only the amount of elementary sulfur required to complete the chemical reaction and attempts to depend on the addition of sodium stearate, sodium oleate, castile soap or sodium resinate, as sole break inducers, satisfactory results were not only unobtainable but a satisfactory break was not obtained even when these compounds were employed in a ratio of 1 to 5000. In comparison to the results above indicated, attention is directed to the results obtained when employing the complex break inducers herein contemplated for use in the doctor treatment.

It is to be noted that the sulfated castor oil was used in a ratio of 1 to 10,000 and the sulfated oleic acid and the phosphorated castor oil in the ations. Figures refer to tests made with 100 gm. ratio of 1 to 5000 and in each case, an excellent portions of gasoline. break was obtained even when there was no sul- Ratio of Mg. oi Actual b k i But lump sulfur re- Mg. of Pea Character of Doctor test Y uii'ed sulfur Break inducer used gg figg break on distillate gg f' g fi g (t eory) used treated 6. 0 6. 0 None 0 None obtained 6.0 7.0 .do 0 .....do 6.0 8.0 0 Good Negative.... Positive 6. 0 6. 0 0. 0002 N no obtained.. 6.0 7.0 0. 0002 air Negative... Positive 6. 0 6. 0 0. 0002 None obtamed.. 6.0 7.0 0.0002 sir Negative.... Positive 6. 0 6. 0 0. 0002 None obtained 6.0 7.0 o 0. 0002 00 Negative.... Positive 6. 0 6. 0 Sodium resinate- 0. 0002 None obtained-- 6.0 7.0 do 0.0002 Fair Negative.... Positive. 6. 0 6. 0 Phosphorated castor oil 0. 0002 do Negative. 6.0. 6.0 Sulfated castor oil 0.0001 00 Do. 6. 0 6. 0 Sulfated oleic acid 0.0002 Good.. d Do.

Examination of the above table emphasizes fur available for break induction, or to say it in the numerous salient points previously discussed. For instance, reference is made to those tests in the above'table which are concerned with the use of the common, rather simple, type of break inducer, to wit, materials such as sodium stearate, sodium oleate, castile soap, sodium resinate and the like.

Furthermore attention is directed to the first three tests which indicate the results obtained when sulfur alone is used as the break inducer. It is to be noted that in the tests as conducted, it was necessary to use six milligrams of sulfur another way. when the amount of sulfur employed was only sufllcient to complete the chemical reactions involved. In each instance, since there was no excess sulfur employed, the butyl mercaptan test obviously has to be negative. Since the butyl mercaptan test had to be negative, it followed that the gasoline was of a type which was free from certain inherently objectionable qualities which are common when there is an excess of elementary sulfur present, or when the gasoline gives a positive butyl mercaptan test. In each instance, the break obtained was the kind characterized as being good, i. e.', appeared'to be satisfactory under any condition of plant operation which one would ordinarily employ.

We have previously indicated that the amount of added break inducer may be as low as one part in 75,000 parts of the oil being sweetened. In practice, however, the amount of break inducer actually present in the oil may be even less than this during certain phases of the process. For example,-in an operation involving recirculation of doctor solution, the ratio of break inducer in the first batch of oil may not exceed one to 30,000 or even one to 45,000 but recycling of the doctor solution once or twice, without further addition of break inducer, may result in an actual ratio of l-80,000 or l-90,000 or even a ratio in excess of l-100,000 in subsequent batches of oil. There- 'it is to be understood that the heretofore mentioned ratio of l-75,000 is not the upper limit of effectiveness, particularly in a recirculation process.

It will be further understood that, instead of employing a single break inducer of the kind herein disclosed, a mixture of two or more of them may be used, if desired. Indeed, the process of manufacture may result in the production of a mixture of a number of break-inducing compounds rather than a single compound in a technically or chemically pure state. Moreover, a break inducer of this invention may be employed in admixture with other types of break inducers for which we have filed separate applications.

Frequently, the compounds of this invention have beneficial effects in addition to bringing about rapid subsidence. For example, as a result of their use, the amount of black strap or feathery material appearing at interfacial surfaces may be greatly diminished or entirely eliminated.

As heretofore stated, the sulfated materials of the present invention are frequently designated as sulfonated oils, sulfonated fatty acids, fatty sulfonates, fatty acid sulfonates, etc. In thus characterizing the materials, the reference is to the method of production rather than to the presence of the typical sulfonic acid radical. As a matter of fact, sulfated fatty materials of the kind herein disclosed as break inducers do not contain any true sulfonic acid radical in detectable or appreciable amount. On the contrary, the non-decomposable organically combined sulfur appears to be present in a sulfone form or the like; In this respect, that is, the substantial absence of the sulfonic acid radical, the break inducers of the present invention are to be distinguished from the true fatty sulfonic acids or their salts contemplated for use as break inducers in our companion application Serial No. 301,828, filed October 28, 1939.

We have herein referred to oil-soluble forms of the sulfated fatty materials. Compounds of this type, particularly adapted for use in the present process, may be produced by reacting the carboxyl radical with an alcohol, such as ethyl, propyl, butyl alcohol or the like, in order to form a half ester. That is to say, the sulfate radical is neutralized in the manner previously described, whereas the carboxyl radical is esterified.

It is to be understood that the detailed disclosures herein are for illustrative purposes only and are not to be considered as limitations on the invention, inasmuch as various modifications within the scope of the appended claims will be apparent to those skilled in the art.

Having described our invention, we claim:

1. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises incorporating into the oil a relatively small amount of a salt of a fatty acid derivative selected from the group consisting of the sulfated and phosphorated fatty substances containing an ester-forming group.

2. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises incorporating into the oil a relatively small amount of a salt of a sulfated fatty substance containing an ester-forming group.

3. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and sufficient elementary sulfur to convert the mercaptans into innocuous compounds, and inducing a break in said treatment by incorporating into the oil a salt of a fatty acid derivative selected from the group consisting of the sulfated and phosphorated fatty substances containing an ester-forming group.

4. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and suiiicient elementary sulfur to convert the mercaptans into innocuous compounds, and inducing a break in said treatment by incorporating into the oil a salt of a sulfated fatty substance containing an ester-forming group.

5. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and a quantity of elementary sulfur not appreciably in excess of the theoretical amount required to convert the mercaptans into innocuous compounds, and inducing a break in said treatment by incorporating into the oil a salt of a fatty acid derivative selected from the group consisting of the sulfated and phosphorated fatty substances containing an ester-forming group.

6. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and a quantity of elementary sulfur not appreciably in excess of the theoretical amount required to convert the mercaptans into innocuous compounds, and inducing a breakin said treatment by incorporating into the oil a salt of a sulfated fatty substance containing an ester-forming group.

7. A method for sweetening hydrocarbon oils containing mercaptans which comprises converting the mercaptans into innocuous compounds by treatment of the oil with alkaline plumbite solution and elementary sulfur, the amount of sulfur being insufiicient to render the oil positive to the butyl mercaptan test and insufiicient to effect settling or subsidence, and inducing a break in said treatment by adding a salt of a fatty acid derivative selected from the group consisting of the sulfated and phosphorated fatty substances containing an ester-forming group.

8. A method for sweetening hydrocarbon oils containing mercaptans which comprises converting the mercaptans into innocuous compounds by treatment of the oil with alkaline plumbite solution and elementary sulfur, the amount of sulfur being insuflicient to render the oil positive to the butyl mercaptans test and insuificient to effect settling or subsidence, and inducing a break in said treatment by adding a salt of a sulfated fatty substance containing an estersulfur, the method of inducing abreak in the doctor treatment which comprises incorporating :into the oil, in a ratio between about 1 to 5000 and 1 to'75,000, a salt of a fatty acid derivative selected from the group consisting of the sulfated and phosphorated fatty substances containing an ester-forming group. 7

10. In a sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises incorporating into the oil, in a ratio between about 1 to 5000 and 1 to 75,000, a salt of a sulfated fatty substance containing an ester-forming group.

11. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition of a sulfatedfatty substance containing an 25 ester-forming group.

12. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementarysulfur, the improvement which comprises facilitating the break in said treatment by the addition of a phosphorated fatty substance containing an ester-forming group.

I 13. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition of sulfated oleic acid.

14. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in and treatment by the addition of sulfated castor oil.

15. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and. elementary sulfur, the improvement which comprises facilitating the break in and treatment by the addition of phosphoratedcastor oil.

CHARLES M. BLAIR, JR. IRA S. BOYDSTUN. 

